Cementing multiple pipe strings in well bores



July 6, 1965 w. J. BlELs'rElN 3,193,010

CEMENTING MULTIPLE PIPE STRINGS IN WELL BORES Filed July 10, 1963 CEMENT SLURRY MUD x CEMENT SLURRY CLJ/L U a lNvENToR. FlG I WALTER J.B|El sTE|N,

BY ATTORNEY.

United States Patent() 3,193,010 CEMENTING MULTIPLE PIPE STRNGS EN WELL BRES Walter J. Bielstein, Corpus Christi, Tex., assigner, by

mesne assignments, to Esso Production Research Company, Houston, Tex., a corporation of Delaware Filed July 10, 1963, Ser. No. 294,037 6 Claims. (Cl. 16o- 21) This invention relates to well cementing, and more particularly to cementing wells wherein a multiplicity of pipe strings are suspended side-by-side in a well bore having no lining or casing.

In recent years it has become practical to eliminate the pipe string that conventionally serves as a lining for well bores penetrating hydrocarbon productive earth formations. In such operations, small diameter pipe strings, commonly referred to as tubing, are cemented in a well bore and perforated to serve as conduits for earth fluids produced from hydrocarbon productive earth formations. Where two or more flow tubings are used in the same well to produce two or more formations, means have been devised for the purpose of singly perforating the tubings after they have been cemented in the well bore. The cement-ing operation is necessary in order to protect water sands to prevent fluid migration between different hydrocarbon productive earth strata and to selectively produce the fluids within the same strata.

In the conventional multiple tubingless completion cementing operation it is the practice to run two or more strings of pipe into the well bore while it is standing at least partially filled with drilling fluid. A cement slurry is then pumped down the longest pipe string and is immediately followed by a wiper plug so that the cement is entirely displaced from the pipe string and occup-ies the annulus between the pipe strings and the wall of the well bore up to a given level in the well bore. After the cement has set to a solid mass, it should prevent fluid communication between the earth formations penetrated by the well bore. However, in many instances it has been found that channels are formed in the set cement, thus, effective seal-ing to prevent fluid migrations between earth formations is not accomplished, nor can the fluids contained in the same formation be selectively produced. This situation becomes increasingly serious as a greater number of pipe strings are disposed in the well bore. One reason for this condition has been found to be that drilling fluid is not displaced from the small space between the pipe strings when three or more pipe strings are disposed in the same well bore, or from between the pipe strings and the sides of the well bore when two or more pipe strings are disposed in the same well bore. It has been found that the cement preferentially displaces the drilling fluid in the large annulus around the pipe strings and simply does not work into the relatively small space between the pipe strings, or between the pipe strings and the sides of the well bore. (The reason that a small space exists between the pipe strings and the sides of the well bore is that well bores are never perfectly vertical, but instead corkscrew down into the earth so that the pipe strings are always laying against the sides of the well bore.) These deposits of mud and mud cake are regions of low strength material. After the pipe strigs have been perforated and production has been initiated, the formation pressure around the perforated interval is reduced, thus creating a substantial pressure differential between the fluid-bearing formation above and below the perforated interval. The deposits of mud and mud cake fail because of their poor strength qualities, and communication with formations above and/or below the producing formation is Fice established. Also, the failure of the low strength areas may result in the operator being unable to selectively produce the fluids within the format-ion perforated.

Another reason that channels are formed in the drilling fluid is that when cement contacts drilling fluid, the drilling fluid is caused to thicken, whereby a viscous layer is formed between the mud and cement bodies. As the cement 4is pumped into the well bore, eventually it will break through the weakest point in this viscous layer, and a long finger or channel of cement will be injected up through the drilling fluid. These channels can be suiliciently long to permit fluid communication between productive earth strata.

In accordance with one aspect of the invention, a plurality of pipe strings are positioned side-by-side in a well bore that is at least partially filled with liquid drilling fluid. In the process of cementing the pipe strings in place in the well bore, first a volume of gas is pumped into one of the strings. This gas is followed by the liquid cement; thus a layer of gas separates the cement and mud as it is pumped down the cement string and up the annulus. As the gas is pumped into the cement string a liquid such as water may be simultaneously injected to aid the scouring action as the gas eX- pands up the hole upon reaching the bottom of the cement string.

Gbjects and features of the invention not apparent from the above discussion will become evident upon consideration of the following description thereof taken in connection with the accompanying drawing, wherein:

FIGS. l and 2 are schematic representations of a portion of an oil or gas well installation illustrating steps in accordance with oneaspect of the invention; and

FIGS. 3 and 4 are cross-sectional views of the borehole shown in FIG. 1 illustrating the relative positions the pipe strings may assume at various points in the borehole.

With reference now to FIG. l, there is shown a borehole 3 extending from the earths surface 1 through the levels -of productive earth strata l() and 29. A conventional multiple completion type of well head apparatus 9 is positioned at the earths surface connected to a string of surface casing S which is cemented t-o the upper portion of the borehole 3 by a cement sheath 7. Three pipe strings 11, I15, and 19 are shown as extending into the borehole, although it is to be understood that tw-o or more pipe strings may be so -disposed in accordance with the invention. Since the lower por-tion of the borehole is shown in section, only two of the pipe strings are illustrated. The pipe strings may all extend to the bottom of the borehole or only one may extend through the lowermost earth formation 20, and the others may extend only through the upper formations which lthey are intended to produce. The pipe strings 11, 15, and 19 are controlled by valves y13, 17, and 21, respectively. Pipe string 19 is illustrated as being connected through valve r2.4 to a pump 25 for pumping a cement slurry into pipe string 19 through line 27. A line 29 is connected to the well head 9 opening into the annulus around the pipe strings so that drilling fluid pumped up the well bore can be exhausted to a mud pit. Line 29 -is -controlled by valve 31. Lines from a source -ofrgasiform fluid lare shown leading -to pipe strings 19 and 11, and it is to be understood lthat a line may be provided leading to pipe string 15'. Each line should be controlled by a separate valve. The gasiforrn fluid should be under substantial pressure and preferably should be a relatively inert ga-s such as nitrogen and carbon dioxide, although -other gases, such as air, may be used. The pipe vstrings are each provided with g-uide shoes at the lower ends thereof; Ithe guide shoes for pipe strings 11 and 19 Iare designated by the reference numerals 33 and verly cemented under conventional practices.

drilling lluid in zones A .andB which it is almost Vimpos-y borehole corkscrews down through 'the earth. For very short distances the pipe strings occasionally may assume the relative positions illustrated in FIG. .4, away from the sides of the borehole. In the relative positions thereof shown in FIG. 3,there will be a small restricted zone A g v Q. the earths surface, and wherein a cementitious fluid is pumped down one of lthe pipe strings and up the annulus Y therearound to bond the pipe s-tringsto the sides of the between the pipe strings and the side of the, borehole. j

When the pipe strings are as illustrated in FIG 4, the restricted zone E between the pipe strings will not'be prop- It is the sible to displace using conventional cementing operations.v Assuming now tha-t the pipe strings are run into the well bore 3 t-o substantially the bottom of the well bore as shown in FIGS. l and 2, valves 2 and 31AY are opened and valve-s -S and 17 are closed. Gas from the source of gasiform fluid is injected into pipe string 19 followed by cement. v

The gas injected in accordance with the present inven-v tion will have no Vdiiculty displacing the mud in zones A and B because of the large Idifferences in density and vis'- lcosity between the displacing Vand the displaced Viiuids. 1

'pipe strings and the spaces between'thepipe strings. As v the cement enters the area in which the gas has kdisplaced the `drilling uid, it in turn -displaces the gas.

Y Itis well Vknown thatl drilling Huid, after circulation Y thereof has ceased for .a period of time, can form a weak gel that is easily broken by further circulation of theV drilling'uid; Gasiform Huid injected in accordance with the invention will have Ysubstantial dificu'lty Vin working up through the gelled drilling liuid. The lower portion of gas bubbles yand it will be possible toVY Vforma .bankfof pure gas beneath the column of drilling Huid and gas out drilling fluid. The entire ldrilling uidcolumn thenfcan be lifted by the gaseous bank. Cement slurry thereupon may be pumped into the bottom of the well bore torlitv the entire column of drilling iiuid asA illustrated inFIG. 2. uid and the cement not only insures more complete' displacement of the drilling tluid fromthe small zones A andr B illustrated in FIGS. 3 and 4, b-ut .also absolutely pre- 1 vents formation of `a crust by commingling vof cement and drilling fluid, with above. K Y Y l In many instances it will be found advantageous to iniect the gasiform fluid. int-o one Iofthe pipel strings dis- The provision of a bank of gas between thedrilling the attendant disadvantages described Vcient in Vvolume to form a'gaseous bank well bore, the improvement comprising: entraining a gasiform 'fluid through :at least the lower portion of the drilling duid in the annulus around the pipe strings and in the space kbetween the pipe'strings; and pumping a bank of saidg-asiform uid down one of the pipe strings sumbetween the cementitious Huid and the drilling'uid.

2.' in a well operation wherein a plurality of pipe strings 'are run Vinto a well bore yat least par-tially til-led withk drilling'uid to coextend side-by-side therein from the earths surface, and wherein a cementiticus fluid is pumped downone ofthepipe strings and up the annulus therearound to bond the pipe strings to the sides of the Well bore, the improvement comprising: pumping a gasiform uid down at leastr'one of the pipestrings before cementitious Vluid is' pumped into the well bore to entrain said t the Idrilling uid column eventually will be saturated with posed in the borehole other than the string to be used for cementing in order to better control the placement of the gas ahead of the cement through the. usual Valve arrangement at the bottoni of the pipe string.

While there has been shown and described what at present is considered to be preferred embodiment of the present invention, other modifications will be apparent to those skilled in the art which do not depart fromtthe scope of the invention as defined What is claimed is:

1. In Va well opera-tion wherein a pluralityV of pipe strings are `run into a well bore atleast partially filled with drilling-fluid to coextend side-byside therein fromV by the appended claims.

- gasiform fluid in the drilling iluid'disposed in theV annulus .around the pipe strings and in the space between the pipe strings; land pumping a bank of gasiform fluid down the pipe string through which cementitious fluidV is to be pumped sufficient in volume to form a gaseous bank betweenrthe cementitious' tluidand the drilling fluid.

3. The method according to claim 2 wherein at least 300 cubic feet of said gasiform -uid measured at standard temperature and pressure is Vinjected into the well bore.

4. The method accordingfto claim 2 wherein the gasiform iiuid is an inert gas.

5, ln a well .cementing operation in `a well bore lhaving drilling liquid therein, the steps comprising:

' Y yrunning at least one pipe string into the well bore;

forming. a bankY of drilling fluid saturated withv bubbles 'of a gasiform luid in the lowermost portion of the f well bore around the pipe string; injecting a bank 'of gasiform.fluidV below said bank of drilling 4uid to displace the bank of Adrilling fluid up the well bore; rand c w Y, Y Y pumping a cementitious lmixture downV theV pipe string to displacevthe'bank of drilling iluid and the bank of gasiform iluid up the well bore. 6. ln a well cementing operation in a well bore having drilling liquid therein, the steps comprising:

runningrat least one pipe stringinto the well bore; pumping'a gasiform uidrdown said pipe stringuntil thedrilling fluid in theflower portion of the well bore is saturated with bubbles ofthe gasiformru-id; pumping additional gasiform fluid down the pipe string Y until a bank of gasiform uid is formed beneath the Qmixture of -dri'lling .fluid andbubbles ofY gasiform iiuid;and' i Y' r y y Y pumping a cementitious mixture down the pipe string to Id-isplacethe bank of gasiform iluid andthe mixture of dr-illingiluid and gasiform fluid up the well bore.

References Cited bythe Examiner VUNITED ysrrarns PATENTS OTHER REFERENCES j Butlington, E. C.: Multi-lur'pose Nitrogen Provides Y New Drillingflool. l In Drilling, 4/62, pp. 54 relied upon` CHARLES E. OCONNELL, Primary Examiner., 

1. IN A WELL OPERATION WHEREIN A PLURALITY OF PIPE STRINGS ARE RUN INTO A WELL BORE AT LEAST PARTIALLY FILLED WITH DRILLING FLUID TO COEXTEND SIDE-BY-SIDE THEREIN FROM THE EARTH''S SURFACE, AND WHEREIN A CEMENTITIOUS FLUID IS PUMPED DOWN ONE OF THE PIPE STRINGS AND UP THE ANNULUS THEREAROUND TO BOND THE PIPE STRINGS TO THE SIDES OF THE WELL BORE, THE IMPROVEMENT COMPRISING: ENTRAINING A GASIFORM FLUID THROUGH AT LEAST THE LOWER PORTION OF THE DRILLING FLUID IN THE ANNULUS AROUND THE PIPE STRINGS AND IN THE SPACE BETWEEN THE PIPE STRINGS; AND PUMPING A BANK OF SAID GASIFORM FLUID DOWN ONE OF THE PIPE STRINGS SUFFICIENT IN VOLUME TO FORM A GASEOUS BANK BETWEEN THE CEMENTITIOUS FLUID AND THE DRILLING FLUID. 